Cement is used in almost all hydrocarbon wells to isolate a section of a pipe string or well bore. The most common cementing operation is to cement a pipe string or casing in a well bore to secure the pipe string and seal off the contents of formations penetrated by the well bore. This is often called primary cementing and involves pumping cement into the casing and then pumping a wiper plug down the casing so it pushes the cement out of the bottom of the casing through a float shoe or collar into which the wiper plug latches. The cement travels upwardly through the annulus between the casing and the well bore and ultimately sets up to secure the casing in the well bore and seal off the formations penetrated by the well bore.
Another common cementing operation occurs when it is necessary or desirable to place cement between casing and the well bore at one or more locations above the bottom of the casing. This almost always occurs at locations that cannot be predicted in advance so the casing is not normally equipped with collars, slots or profiles in which squeeze equipment can be latched. Thus, squeeze operations are normally conducted through perforations in the casing. Often, the perforations open into a hydrocarbon bearing formation and it is desirable to squeeze cement through the perforations to isolate the formation. Squeeze operations are also conducted to repair a poor primary cement job by squeezing cement into areas where cement is poor or non-existent. Conventionally, a cement retainer is run on the bottom of a work string and comprises slips to set the retainer against the casing, a seal to seal between the casing and the cement retainer and an actuable valve that can be opened by manipulation of the work string to allow cement to be pumped through the cement retainer and through the perforations. After a desired amount of cement is pumped through the cement retainer, an amount of water or completion fluid is pumped into the work string to displace cement in the work string and cement retainer. After the cement sets up, the cement retainer and work string are pulled from the casing. Naming this tool a cement retainer is quite descriptive because its function is to retain cement behind the casing and prevent it from flowing back into the inside of the casing.
In some areas, it is very difficult to get good cement jobs on surface pipe or intermediate casing at shallow depths. This almost surely has something to do with the unconsolidated nature of shallow formations. Whatever the reason, it often occurs that long stretches of casing are poorly cemented, meaning that many squeeze jobs are necessary to provide adequate cement between the casing and the well bore. This is a slow operation because the cement must be allowed sufficient time to set up before pulling the cement retainer and work string, shooting a new set of perforations, running a new or redressed cement retainer back into the well on the work string to a location above the new perforations before pumping cement through the new set of perforations. Typically, only one squeeze job can be conducted in a 3-5 hour period at 4000′. The time to conduct a conventional squeeze operation is a function of depth because of the time to run a work string into the well and to retrieve it.
Disclosures of interest are found in U.S. Pat. Nos. 2,196,661; 3,921,720; 3,713,486; 4,133,386; 7,428,927 and 7,861,781 and Printed U.S. Patent Applications 20100193190 and 20110162844.